Alkylene glycols, in particular monoalkylene glycols, are of established commercial interest. For example, monoalkylene glycols are being used in anti-freeze compositions, as solvents and as base materials in the production of polyalkylene terephthalates e.g. for fibers or bottles.
The production of alkylene glycols by liquid phase hydrolysis of alkylene oxide is known. The hydrolysis is performed without a catalyst by adding a large excess of water, e.g. 20 to 25 moles of water per mole of alkylene oxide, or with a smaller excess of water in a catalytic system. The reaction is considered to be a nucleophilic substitution reaction, whereby opening of the alkylene oxide ring occurs, water acting as the nucleophile. Because the primarily formed monoalkylene glycol also acts as a nucleophile, as a rule, a mixture of monoalkylene glycol, dialkylene glycol and higher alkylene glycols is formed. In order to increase the selectivity to monoalkylene glycol, it is necessary to suppress the secondary reaction between the primary product and the alkylene oxide, which competes with the hydrolysis of the alkylene oxide.
One effective means for suppressing the secondary reaction is to increase the relative amount of water present in the reaction mixture. Although this measure improves the selectivity towards the production of the monoalkylene glycol, it creates a problem in that large amounts of water have to be removed for recovering the product.
Considerable efforts have been made to find an alternative for increasing the reaction selectivity without having to use a large excess of water. Usually these efforts have focused on the selection of more active hydrolysis catalysts. The use of homogeneous catalysts can be particularly beneficial in the hydration of alkylene oxide if they can easily be separated from the reaction product. However, the use of catalysts in homogeneous reaction systems generally pose a problem when the reaction product is separated by distillation due to the low solubility of the catalyst compounds in the glycol product. The low solubility of the catalyst can result in the precipitation thereof during the separation of the reaction product.
An important step in the manufacture of alkylene glycol by the catalytic hydrolysis of alkylene oxide is the separation of the water, catalyst and reaction by-products from the alkylene glycol reaction product. It is thus necessary for the homogeneous catalyst used in such a process to have properties which permit the easy separation of the alkylene glycol from the other components of the reaction product.
Accordingly, there is a need to develop a process that uses an active but selective alkylene oxide hydration catalyst having solubility characteristics which permit easy separation of the alkylene glycol reaction product and other components of the reaction product for reuse in the hydration reaction.
Other aspects, objects, and the several advantages of the invention will become apparent in light of the following disclosure.